Method and system for measuring a wideband loop sensitivity for an acoustic transducer

ABSTRACT

A method and system is disclosed for measuring a wideband loop sensitivity S L (f) for an acoustic transducer in an acoustic probe. A pulse signal is employed as a wideband reference signal V r (t); and, in a pulse-echo measurement a corresponding wideband echo signal V e (t) is obtained. A normalized loop frequency response {circumflex over (X)}(f) for the acoustic transducer is defined as a ratio of a Fourier Transform of the V e (t) to a Fourier Transform of the V r (t). A wideband loop sensitivity S L (f) for the acoustic transducer is defined as an absolute square of the {circumflex over (X)}(f) in decibel.

RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.15/855,677, filed Dec. 27, 2017, the disclosure of which is herebyincorporated by reference herein in its entirety.

BACKGROUND Technical Field

The present invention relates to a method and system for measuring awideband loop sensitivity for an acoustic transducer in an acousticprobe.

Description of Related Art

An acoustic transducer is a key component in an acoustic imaging system.The technologies of acoustic imaging have been frequently employed tonon-destructive testing, clinical diagnosis, and under waterapplications due to such advantages of acoustic imaging as non-invasive,non-ionization, real-time imaging, and cost-effectiveness. For example,acoustic imaging for clinical diagnosis, which is used for assessing thesoft tissue structure and blood flow, is currently the most usedclinical imaging modality after conventional X-ray radiography.

FIGS. 1A˜1B show a typical structure for an acoustic probe in a priorart. An acoustic probe 113 has a transducer array 117A which comprises aplurality of acoustic transducer 117. The number of acoustic transducer117 in the transducer array 117A is greater than or equal to one.

In the prior art, a sensitivity is used to assess the characteristics ofan acoustic transducer 117. FIGS. 2A˜2B show the method of sensitivitymeasurement for an acoustic transducer in an acoustic probe in a priorart. FIG. 2A shows a measuring arrangement for reference signal in aprior art. A sine burst generator 200 is arranged to output a sine burstsignal at a specific frequency on an external 50-ohm load as a referencesignal V_(r)(t) 204. FIG. 2B shows a measuring arrangement for anacoustic probe 113 in a prior art. The sine burst generator 200 iselectrically coupled to an acoustic probe 113 which is immersed in awater bath 208 with an acoustic mirror 212. The acoustic probe 113 isdriven by the sine burst generator 200 and transmits an acoustic sineburst wave 214 at the specific frequency. The acoustic probe 113receives the reflected sine burst wave 218 from the acoustic mirror 212and outputs an echo signal V_(e)(t) 224.

FIG. 3A shows a reference signal for an acoustic probe in a prior art.The reference signal V_(r)(t) 204 is a sine burst signal with aminimum-run of 15 cycles at a specific frequency; and, a peak-to-peakvoltage of reference signal (V_(ppr)) is obtained. FIG. 3B shows an echosignal for an acoustic probe in a prior art. The echo signal V_(e)(t)224 is a sine burst signal at the specific frequency; and a peak-to-peakvoltage of echo signal (V_(ppe)) is obtained. A loop sensitivity for theacoustic transducer is calculated based upon the peak-to-peak voltage ofecho signal (V_(ppe)) to the peak-to-peak voltage of reference signal(V_(ppr)).

The disadvantage for the prior art is that one specific frequency isadopted for measuring a loop sensitivity of an acoustic transducer 117in an acoustic probe 113. In an early stage, traditional acoustic proberesponds to narrow band frequency only. However, wideband acoustic probehas been developed due to rapid progress in the acoustic technologydevelopment in recent years. Therefore, there is a general need for amethod and system for measuring wideband characteristics of an acoustictransducer such as normalized loop frequency response {circumflex over(X)}(f) and wideband loop sensitivity S_(L)(n.

SUMMARY

The present invention discloses a method and system for measuringwideband characteristics of an acoustic transducer in an acoustic probe;the wideband characteristics include normalized loop frequency response{circumflex over (X)}(f) and wideband loop sensitivity S_(L)(f).

A method for measuring a wideband loop sensitivity for an acoustictransducer in an acoustic probe is introduced according to the presentinvention.

A pulse generator of 50-ohm source impedance, which is used to generateunipolar pulse and/or bipolar pulse, electrically couples to an external50-ohm load to obtain a wideband reference signal V_(r)(t) on the 50-ohmload and further obtain a function {circumflex over (V)}_(r)(f) that isa Fourier Transform of the wideband reference signal V_(r)(t).

In a first and a second embodiment, the adopted pulse is anegative-going unipolar pulse and positive-going unipolar pulse,respectively; and in a third and a fourth embodiment, the adopted pulseis a negative-positive bipolar pulse and positive-negative bipolarpulse, respectively.

The pulse generator of 50-ohm source impedance electrically couples toan acoustic probe for measuring the wideband characteristics of anacoustic transducer. The acoustic probe is immersed into a water bathwith an acoustic mirror. The acoustic probe is aligned so that theacoustic wave is normally incident to and reflected from the acousticmirror. An acoustic transducer in the acoustic probe is driven by thepulse generator of 50-ohm source impedance and transmits a widebandacoustic wave toward the acoustic mirror. The transmitted widebandacoustic wave travels and reaches the acoustic mirror and is reflectedbackward to the acoustic transducer in the water bath. The acoustictransducer receives the reflected wideband acoustic wave and outputs awideband echo signal V_(e) (t); and, a function {circumflex over(V)}_(e)(f) that is a Fourier Transform of the wideband echo signalV_(e)(t) is obtained.

A normalized loop frequency response {circumflex over (X)}(f) of theacoustic transducer is defined as the ratio of the function {circumflexover (V)}_(e) (f) to the function {circumflex over (V)}_(r)(f); that is,

${{\hat{X}(f)}\overset{def}{=}\frac{{\hat{V}}_{e}(f)}{{\hat{V}}_{r}(f)}},$according to the present invention.

A wideband loop sensitivity S_(L)(f) for the acoustic transducer isdefined as the following:S _(L)(f)

10 log|{circumflex over (X)}(f)|²,according to the present invention.

Furthermore, obtain a plurality of wideband loop sensitivity S_(L)(f)for each and all acoustic transducers in the acoustic probe byperforming the measuring step for calculating the wideband loopsensitivity S_(L)(f) sequentially or randomly over each and all acoustictransducers in the acoustic probe according to the present invention.

The important parameters of an acoustic transducer such as central orresonant frequency, frequency bandwidth, and averaged wideband loopsensitivity can be obtained from the wideband loop sensitivity S_(L)(n.

The method for measuring the wideband loop sensitivity S_(L)(f) for anacoustic transducer and method for measuring the plurality of widebandloop sensitivity S_(L)(f) for each and all acoustic transducers in theacoustic probe are embedded in one of the firmware and the programmemory; and, all data of measurement are stored in the storage andoutput to output devices that is electrically coupled to the controlunit, according to the present invention.

A system for measuring a wideband loop sensitivity for an acoustictransducer in an acoustic probe is introduced according to the presentinvention. The system comprises a pulse generator, a signal processingunit, a transducer selector, and a control unit. The control unitfurther comprises a firmware, a program memory, and a storage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A˜1B show a typical structure for an acoustic probe in a priorart.

FIG. 2A shows a measuring arrangement for reference signal in a priorart.

FIG. 2B shows a measuring arrangement for an acoustic probe in a priorart.

FIG. 3A shows a reference signal for an acoustic probe in a prior art.

FIG. 3B shows an echo signal for an acoustic probe in a prior art.

FIGS. 4A˜4B show a negative-going unipolar pulse used as a widebandreference signal and its energy spectrum for a first embodimentaccording to the present invention.

FIGS. 5A˜5B show a positive-going unipolar pulse used as a widebandreference signal and its energy spectrum for a second embodimentaccording to the present invention.

FIG. 6A shows a typical energy spectrum of wideband reference signalbased on a unipolar pulse signal for a first and second embodimentsaccording to the present invention.

FIG. 6B shows a typical frequency response for an acoustic transducer inthe first and second embodiments according to the present invention.

FIGS. 7A˜7B show a negative-positive bipolar pulse used as a widebandreference signal and its energy spectrum for a third embodimentaccording to the present invention.

FIGS. 8A˜8B show a positive-negative bipolar pulse used as a widebandreference signal and its energy spectrum for a fourth embodimentaccording to the present invention.

FIG. 9A shows a typical energy spectrum of wideband reference signalbased on a bipolar pulse signal for the third and fourth embodimentsaccording to the present invention.

FIG. 9B shows a typical frequency response for an acoustic transducer inthe third and fourth embodiments according to the present invention.

FIG. 10A shows a measuring arrangement for a wideband reference signalaccording to the present invention.

FIG. 10B shows a measuring arrangement for an acoustic probe accordingto the present invention.

FIG. 11A shows an electrical waveform of a wideband reference signal andits Fourier Transform according to the present invention based on anegative-going unipolar pulse for a first embodiment.

FIG. 11B shows an electrical waveform of a wideband echo signal and itsFourier Transform according to the present invention based on thenegative-going unipolar pulse for the first embodiment.

FIG. 12A shows an electrical waveform of a wideband reference signal andits Fourier Transform according to the present invention based on apositive-going unipolar pulse for a second embodiment.

FIG. 12B shows an electrical waveform of a wideband echo signal and itsFourier Transform according to the present invention based on thepositive-going unipolar pulse for the second embodiment.

FIG. 13A shows an electrical waveform of a wideband reference signal andits Fourier Transform according to the present invention based on afirst bipolar pulse for a third embodiment.

FIG. 13B shows an electrical waveform of a wideband echo signal and itsFourier Transform according to the present invention based on the firstbipolar pulse for the third embodiment.

FIG. 14A shows an electrical waveform of a wideband reference signal andits Fourier Transform according to the present invention based on asecond bipolar pulse for a fourth embodiment.

FIG. 14B shows an electrical waveform of a wideband echo signal and itsFourier Transform according to the present invention based on the secondbipolar pulse for the fourth embodiment.

FIG. 15 shows a flow chart for measuring a wideband loop sensitivity ofan acoustic transducer according to the present invention.

FIG. 16A shows a measured curve of wideband loop sensitivity versusfrequency that is obtained in a one-shot measurement for an acoustictransducer according to the present invention.

FIG. 16B shows a table of selected readings from the measured curve ofwideband loop sensitivity versus frequency that is obtained in aone-shot measurement for an acoustic transducer according to the presentinvention.

FIG. 17 shows a system for measuring a wideband loop sensitivity of anacoustic transducer in an acoustic probe according to the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention discloses a method and system for measuringwideband characteristics of an acoustic transducer in an acoustic probe;the wideband characteristics includes normalized loop frequency response{circumflex over (X)}(f) and wideband loop sensitivity S_(L)(f). The“loop” means the pulse-echo mode in which an acoustic transducertransmits an acoustic wave out and a corresponding reflected echo waveis received by the same acoustic transducer.

A method for measuring a wideband loop sensitivity for an acoustictransducer in an acoustic probe is introduced according to the presentinvention.

A pulse signal is adopted as a wideband reference signal V_(r)(t) formeasuring wideband characteristics of an acoustic transducer accordingto the present invention. There are four embodiments of adopted pulsesignal used in the present invention, which include a negative-goingunipolar pulse 400 for a first embodiment, a positive-going unipolarpulse 500 for a second embodiment, a negative-positive bipolar pulse 700for a third embodiment, and a positive-negative bipolar pulse 800 for afourth embodiment, according to the present invention.

FIGS. 4A˜4B show a negative-going unipolar pulse used as a widebandreference signal and its energy spectrum for a first embodimentaccording to the present invention. The wideband reference signalV_(r)(t) of negative-going unipolar pulse 400 is adopted in the firstembodiment, and an energy spectrum of wideband reference signal1/50|{circumflex over (V)}_(r)(f)|² of negative-going unipolar pulse 404is obtained, in which the function {circumflex over (V)}_(r)(f) is aFourier Transform of the wideband reference signal V_(r)(t) ofnegative-going unipolar pulse 400.

FIGS. 5A˜5B show a positive-going unipolar pulse used as a widebandreference signal and its energy spectrum for a second embodimentaccording to the present invention. The wideband reference signalV_(r)(t) of positive-going unipolar pulse 500 is adopted in the secondembodiment, and an energy spectrum of wideband reference signal1/50|{circumflex over (V)}_(r)(f)|² of positive-going unipolar pulse 504is obtained, in which the function {circumflex over (V)}_(r)(f) is aFourier Transform of the wideband reference signal V_(r)(t) ofpositive-going unipolar pulse 500.

FIG. 6A shows a typical energy spectrum of wideband reference signalbased on a unipolar pulse signal for the first and second embodimentsaccording to the present invention. A maximum energy spectrum density ofthe energy spectrum of wideband reference signal 404, 504 is at 0 Hz(f₀). An upper bound frequency (f₄) of the energy spectrum of widebandreference signal 404, 504 is a frequency where the energy spectrumdensity drops down to a certain decibel value (e.g., −6 dB) relative tothe maximum energy spectrum density at 0 Hz (f₀).

FIG. 6B shows a typical frequency response for an acoustic transducer inthe first and second embodiments according to the present invention. Amaximum frequency response of an acoustic transducer is usually at itscentral frequency or resonant frequency. The upper bound frequency (f₃)and lower bound frequency (f₂) for the frequency response of acoustictransducer 600 are frequencies where the frequency response drops downto a certain decibel value (e.g., −6 dB) relative to its maximumresponse located at between (f₂) and (f₃), respectively.

To assure a good signal-to-noise ratio for the measurement in the firstand second embodiments, the requirement is that the upper boundfrequency (f₄) of the energy spectrum of wideband reference signal 404,504 is greater than the upper bound frequency (f₃) of the frequencyresponse of the acoustic transducer 600, that is, f₄>f₃, according tothe present invention.

FIGS. 7A˜7B show a negative-positive bipolar pulse used as a widebandreference signal and its energy spectrum for a third embodimentaccording to the present invention. The wideband reference signalV_(r)(t) of negative-positive bipolar pulse 700 is adopted in the thirdembodiment, and an energy spectrum of wideband reference signal1/50|{circumflex over (V)}_(r)(f)|² of negative-positive bipolar pulse704 is obtained, in which the function {circumflex over (V)}_(r)(f) is aFourier Transform of the wideband reference signal V_(r)(t) ofnegative-positive bipolar pulse 700.

FIGS. 8A˜8B show a positive-negative bipolar pulse used as a widebandreference signal and its energy spectrum for a fourth embodimentaccording to the present invention. The wideband reference signalV_(r)(t) of positive-negative bipolar pulse 800 is adopted in the fourthembodiment, and an energy spectrum of wideband reference signal1/50|{circumflex over (V)}_(r)(f)|² of positive-negative bipolar pulse804 is obtained, in which the function {circumflex over (V)}_(r)(f) is aFourier Transform of the wideband reference signal V_(r)(t) ofpositive-negative bipolar pulse 800.

FIG. 9A shows a typical energy spectrum of wideband reference signalbased on a bipolar pulse signal for the third and fourth embodimentsaccording to the present invention. The lower bound frequency (f₁) andupper bound frequency (f₄) of the energy spectrum of wideband referencesignal 704, 804 are frequencies where the energy spectrum density dropsdown to a certain decibel value (e.g., −6 dB) relative to its maximumlocated at between (f₁) and (f₄), respectively.

FIG. 9B shows a typical frequency response for an acoustic transducer inthe third and fourth embodiments according to the present invention. Amaximum frequency response for the acoustic transducer is usually at itscentral frequency or resonant frequency. The upper bound frequency (f₃)and lower bound frequency (f₂) for the frequency response of acoustictransducer 900 are frequencies where the frequency response drops downto a certain decibel value (e.g., −6 dB) relative to its maximumresponse located at between (f₂) and (f₃), respectively.

To assure a good signal-to-noise ratio for the measurement in the thirdand fourth embodiments, the requirement is that the upper boundfrequency (f₄) of the energy spectrum of wideband reference signal 704,804 is greater than the upper bound frequency (f₃) of the frequencyresponse of the acoustic transducer 900 and the lower bound frequency(f₁) of the energy spectrum of wideband reference signal 704, 804 issmaller than the lower bound frequency (f₂) of the frequency response ofthe acoustic transducer 900; that is, f₄>f₃>f₂>f₁, according to thepresent invention.

FIG. 10A shows a measuring arrangement for a wideband reference signalaccording to the present invention. An external 50-ohm load iselectrically coupled to a pulse generator of 50-ohm source impedance1000 that generates unipolar pulse and/or bipolar pulse to obtain awideband reference signal V_(r)(t) 400, 500, 700, 800 on the 50-ohmload.

FIG. 10B shows a measuring arrangement for an acoustic probe accordingto the present invention. The pulse generator of 50-ohm source impedance1000 electrically couples to an acoustic probe 113 for measuring thewideband characteristics of an acoustic transducer 117. The acousticprobe 113 is immersed into a water bath 208 with an acoustic mirror 212.The acoustic probe 113 is aligned so that the acoustic wave is normallyincident to and reflected from the acoustic mirror 212. An acoustictransducer 117 in the acoustic probe 113 is driven by the pulsegenerator of 50-ohm source impedance 1000 and transmits a widebandacoustic wave toward the acoustic mirror 212. The transmitted widebandacoustic wave 1004 travels and reaches the acoustic mirror 212 in thewater bath 208 and is reflected backward to the acoustic transducer 117.The acoustic transducer 117 receives the reflected wideband acousticwave 1008 and outputs a wideband echo signal V_(e)(t) 1100, 1200, 1300,1400 respectively in the four embodiments.

FIG. 11A shows an electrical waveform of a wideband reference signal andits Fourier Transform according to the present invention based on anegative-going unipolar pulse for a first embodiment. The widebandreference signal V_(r)(t) of negative-going unipolar pulse 400 isadopted in the first embodiment and a function {circumflex over(V)}_(r)(f), that is a Fourier Transform of the wideband referencesignal V_(r) (t) of negative-going unipolar pulse 400, is obtained.Meanwhile, an energy of reference signal (E_(r)) for wideband referencesignal V_(r)(t) of negative-going unipolar pulse 400 is calculated asone of a time-integral of the power of wideband reference signal and afrequency-integral of the energy spectrum density of wideband referencesignal; that is,E _(r)= 1/50∫V _(r)(t)² dt= 1/50∫|{circumflex over (V)} _(r)(f)|² df.

FIG. 11B shows an electrical waveform of a wideband echo signal and itsFourier Transform according to the present invention based on thenegative-going unipolar pulse for the first embodiment. A wideband echosignal V_(e)(t) based on negative-going unipolar pulse 1100 is obtainedin the first embodiment and a function {circumflex over (V)}_(e)(f),that is a Fourier Transform of the wideband echo signal V_(e)(t) basedon negative-going unipolar pulse 1100, is further obtained. Meanwhile,an energy of echo signal (E_(e)) for wideband echo signal V_(e)(t) basedon negative-going unipolar pulse 1100 is calculated as one of atime-integral of the power of wideband echo signal and afrequency-integral of the energy spectrum density of wideband echosignal; that is,E _(e)= 1/50∫V _(e)(t)² dt= 1/50∫|{circumflex over (V)} _(e)(f)|² df.

FIG. 12A shows an electrical waveform of a wideband reference signal andits Fourier Transform according to the present invention based on apositive-going unipolar pulse for a second embodiment. The widebandreference signal V_(r) (t) of positive-going unipolar pulse 500 isadopted in the second embodiment and a function {circumflex over(V)}_(r)(f), that is a Fourier Transform of the wideband referencesignal V_(r) (t) of positive-going unipolar pulse 500, is obtained.Meanwhile, an energy of reference signal (E_(r)) for wideband referencesignal V_(r) (t) of positive-going unipolar pulse 500 is calculated asone of a time-integral of the power of wideband reference signal and afrequency-integral of the energy spectrum density of wideband referencesignal; that is,E _(r)= 1/50∫V _(r)(t)² dt= 1/50∫|{circumflex over (V)} _(r)(f)|² df.

FIG. 12B shows an electrical waveform of a wideband echo signal and itsFourier Transform according to the present invention based on thepositive-going unipolar pulse for the second embodiment. A wideband echosignal V_(e)(t) based on positive-going unipolar pulse 1200 is obtainedin the second embodiment and a function {circumflex over (V)}_(e)(f),that is a Fourier Transform of the wideband echo signal V_(e) based onpositive-going unipolar pulse 1200, is further obtained. Meanwhile, anenergy of echo signal (E_(e)) for wideband echo signal V_(e)(t) based onpositive-going unipolar pulse 1200 is calculated as one of atime-integral of the power of wideband echo signal and afrequency-integral of the energy spectrum density of wideband echosignal; that is,E _(e)= 1/50∫V _(e)(t)² dt= 1/50∫|{circumflex over (V)} _(e)(f)|² df.

FIG. 13A shows an electrical waveform of a wideband reference signal andits Fourier Transform according to the present invention based on afirst bipolar pulse for a third embodiment. The wideband referencesignal V_(r)(t) of negative-positive bipolar pulse 700 is adopted in thethird embodiment and a function {circumflex over (V)}_(r) (n, that is aFourier Transform of the wideband reference signal V_(r)(t) ofnegative-positive bipolar pulse 700, is obtained. Meanwhile, an energyof reference signal (E_(r)) for wideband reference signal V_(r)(t) ofnegative-positive bipolar pulse 700 is calculated as one of atime-integral of the power of wideband reference signal and afrequency-integral of the energy spectrum density of wideband referencesignal; that is,E _(r)= 1/50∫V _(r)(t)² dt= 1/50∫|{circumflex over (V)} _(r)(f)|² df.

FIG. 13B shows an electrical waveform of a wideband echo signal and itsFourier Transform according to the present invention based on the firstbipolar pulse for the third embodiment. A wideband echo signal V_(e)(t)based on negative-positive bipolar pulse 1300 is obtained in the thirdembodiment and a function {circumflex over (V)}_(e)(f), that is aFourier Transform of the wideband echo signal V_(e)(t) based onnegative-positive bipolar pulse 1300, is further obtained. Meanwhile, anenergy of echo signal (E_(e)) for wideband echo signal V_(e)(t) based onnegative-positive bipolar pulse 1300 is calculated as one of atime-integral of the power of wideband echo signal and afrequency-integral of the energy spectrum density of wideband echosignal; that is,E _(e)= 1/50∫V _(e)(t)² dt= 1/50∫|{circumflex over (V)} _(e)(f)|² df.

FIG. 14A shows an electrical waveform of a wideband reference signal andits Fourier Transform according to the present invention based on asecond bipolar pulse for a fourth embodiment. The wideband referencesignal V_(r)(t) of positive-negative bipolar pulse 800 is adopted in thefourth embodiment and a function {circumflex over (V)}_(r)(f), that is aFourier Transform of the wideband reference signal V_(r)(t) ofpositive-negative bipolar pulse 800, is obtained. Meanwhile, an energyof reference signal (E_(r)) for wideband reference signal V_(r)(t) ofpositive-negative bipolar pulse 800 is calculated as one of atime-integral of the power of wideband reference signal and afrequency-integral of the energy spectrum density of wideband referencesignal; that is,E _(r)= 1/50∫V _(r)(t)² dt= 1/50∫|{circumflex over (V)} _(r)(f)|² df.

FIG. 14B shows an electrical waveform of a wideband echo signal and itsFourier Transform according to the present invention based on the secondbipolar pulse for the fourth embodiment. A wideband echo signal V_(e)(t)based on positive-negative bipolar pulse 1400 is obtained in the fourthembodiment and a function {circumflex over (V)}_(e)(f), that is aFourier Transform of the wideband echo signal V_(e) (t) based onpositive-negative bipolar pulse 1400, is further obtained. Meanwhile, anenergy of echo signal (E_(e)) for wideband echo signal V_(e)(t) based onpositive-negative bipolar pulse 1400 is calculated as one of atime-integral of the power of wideband echo signal and afrequency-integral of the energy spectrum density of wideband echosignal; that is,E _(e)= 1/50∫V _(e)(t)² dt= 1/50∫|{circumflex over (V)} _(e)(f)|² df.

A normalized loop frequency response {circumflex over (X)}(f) for theacoustic transducer is defined as a ratio of the function {circumflexover (V)}_(e)(f) which is a Fourier Transform of the wideband echosignal V_(e) (t) to the function {circumflex over (V)}_(r)(f) which is aFourier Transform of the wideband reference signal V_(r)(t); that is,

${{\hat{X}(f)}\overset{def}{=}\frac{{\hat{V}}_{e}(f)}{{\hat{V}}_{r}(f)}},$according to the present invention.

A wideband loop sensitivity S_(L)(f) for the acoustic transducer isdefined as an absolute square of the normalized loop frequency response{circumflex over (X)}(f) in decibel; that is, S_(L)(f)

10 log|{circumflex over (X)}(f)|², according to the present invention.

FIG. 15 shows a flow chart for measuring a wideband loop sensitivity ofan acoustic transducer according to the present invention.

The measuring step for obtaining and storing a function {circumflex over(V)}_(r)(f) that is a Fourier Transform of a wideband reference signalV_(r)(t) comprises:

-   -   preparing a pulse generator and a signal processing unit;    -   generating a pulse to create a wideband signal as a reference        signal;    -   obtaining a wideband reference signal V_(r)(t);    -   obtaining a function {circumflex over (V)}_(r)(f) that is a        Fourier Transform of the wideband reference signal V_(r)(t); and    -   storing the function {circumflex over (V)}_(r)(f) that is a        Fourier Transform of the wideband reference signal V_(r)(t) in        one of a firmware and a program memory.

The pulse is one of a unipolar pulse and a bipolar pulse. The unipolarpulse is one of a negative-going pulse 400 and a positive-going pulse500. The bipolar pulse is one of a negative-positive bipolar pulse 700and a positive-negative bipolar pulse 800.

The measuring step for obtaining and storing a function {circumflex over(V)}_(e)(f) that is a Fourier Transform of a wideband echo signalV_(e)(t) comprises:

-   -   coupling the pulse generator and the signal processing unit to        an acoustic transducer;    -   generating a wideband acoustic wave from the acoustic        transducer;    -   obtaining a wideband echo signal V_(e)(t) after the acoustic        wave being reflected from an acoustic mirror;    -   obtaining a function {circumflex over (V)}_(e)(f) that is a        Fourier Transform of the wideband echo signal V_(e)(t); and    -   storing the function {circumflex over (V)}_(e)(f) in a program        memory.

The measuring step for defining a normalized loop frequency response{circumflex over (X)}(f) for the acoustic transducer comprises:

-   -   obtaining the function {circumflex over (V)}_(r)(f) that is a        Fourier Transform of the wideband reference signal V_(r)(t);    -   obtaining the function {circumflex over (V)}_(e)(f) that is a        Fourier Transform of the wideband echo signal V_(e)(t);    -   defining a normalized loop frequency response {circumflex over        (X)}(f) as follows:

${{\hat{X}(f)}\overset{def}{=}\frac{{\hat{V}}_{e}(f)}{{\hat{V}}_{r}(f)}};$and

-   -   storing the normalized loop frequency response {circumflex over        (X)}(f) in the program memory.

The measuring step for defining a wideband loop sensitivity S_(L)(f) forthe acoustic transducer comprises:

-   -   obtaining the normalized loop frequency response {circumflex        over (X)}(f);    -   defining a wideband loop sensitivity S_(L)(f) which is a        function of frequency for the acoustic transducer as follows:        S _(L)(f)        10 log|{circumflex over (X)}(f)|²;    -   storing the wideband loop sensitivity S_(L)(f) in a storage        device; and    -   outputting data stored in the storage device.

Furthermore, obtain a plurality of wideband loop sensitivity S_(L)(f)for each and all acoustic transducers in an acoustic transducer array;the measuring step for which comprises:

-   -   performing the measuring step for calculating the wideband loop        sensitivity S_(L)(f) sequentially or randomly over each and all        acoustic transducers in an acoustic transducer array;    -   obtaining a plurality of wideband loop sensitivity S_(L)(f);    -   storing the plurality of wideband loop sensitivity S_(L)(f) in        the storage device; and    -   outputting data stored in the storage device.

An example of measuring a wideband loop sensitivity of an acoustictransducer in an acoustic probe was performed according to the presentinvention and the results are shown in FIGS. 16A˜16B. FIG. 16A shows ameasured curve of wideband loop sensitivity versus frequency that isobtained in a one-shot measurement for an acoustic transducer accordingto the present invention. From the measured curve of wideband loopsensitivity versus frequency, some important parameters of the acoustictransducer can be observed; for instance, the central frequency orresonant frequency is at the vicinity of 7.3 MHz, the fractionalbandwidth over −6 dB is around 80%, and the averaged wideband loopsensitivity over −6 dB bandwidth is −49.9 dB.

FIG. 16B shows a table of selected readings from the measured curve ofwideband loop sensitivity versus frequency that is obtained in aone-shot measurement for an acoustic transducer according to the presentinvention. The selected readings of loop sensitivity versus frequencyinclude −60 dB at 4 MHz, −47 dB at 6 MHz, −47 dB at 8 MHz, −51 dB at 10MHz, and −66 dB at 12 MHz etc.

The acoustic transducer under test in the example is in a transducerarray of a commercial acoustic probe containing one hundred andninety-two (192) acoustic transducers. In the measurement, anegative-going unipolar pulse with an amplitude of −75 volts and anupper bound frequency of 55 MHz was adopted as a wideband referencesignal. The distance between the acoustic transducer and acoustic mirroris 20 mm. And, the material of the acoustic mirror is stainless-steelwith an acoustic reflection coefficient of 0.93 in a water bath.

FIG. 17 shows a system for measuring a wideband loop sensitivity for anacoustic transducer in an acoustic probe according to the presentinvention. The system 1700 comprises a pulse generator 1701, a signalprocessing unit 1702, a transducer selector 1704, and a control unit1706. The control unit 1706 further comprises a firmware 1707, a programmemory 1708, and a storage 1709.

The control unit 1706 electrically couples to the pulse generator 1701,to the signal processing unit 1702, and to the external output devices1730.

The pulse generator 1701 is electrically coupled to an acoustictransducer through the transducer selector 1704 for generating a pulseto create a wideband acoustic wave from the acoustic transducer. Thepulse is one of a unipolar pulse and a bipolar pulse. The unipolar pulseis one of a negative-going pulse 400 and a positive-going pulse 500. Thebipolar pulse is one of a negative-going pulse first and apositive-going pulse second 700 and a positive-going pulse first and anegative-going pulse second 800.

The reflected wideband echo wave is received by the acoustic transducerthrough the transducer selector 1704 to the signal processing unit 1702for further processing. The transducer selector 1704 sequentially orrandomly selects one transducer of a transducer array in an acousticprobe 113 for measuring.

The measuring method for obtaining a function {circumflex over(V)}_(r)(f) that is a Fourier Transform of a wideband reference signalV_(r)(t) is embedded in one of the firmware 1707 and the program memory1708 according to the present invention.

The measuring method for obtaining a function {circumflex over (V)}_(e)(f) that is a Fourier Transform of the wideband echo signal V_(e)(t) isembedded in one of the firmware 1707 and the program memory 1708according to the present invention.

The method for measuring a wideband loop sensitivity S_(L)(f) for theacoustic transducer is embedded in one of the firmware 1707 and theprogram memory 1708 according to the present invention.

The method for measuring the plurality of wideband loop sensitivityS_(L)(f) for each and all acoustic transducers in an acoustic transducerarray is embedded in one of the firmware 1707 and the program memory1708 according to the present invention.

All data of measurement are stored in the storage 1709 and can be outputto the output devices 1730 according to the present in invention.

The present invention discloses a method and system for measuringwideband characteristics of an acoustic transducer in an acoustic probe,the wideband characteristics includes normalized loop frequency response{circumflex over (X)}(f) and wideband loop sensitivity S_(L)(f). Theimportant parameters of an acoustic transducer such as central frequencyor resonant frequency, frequency bandwidth, and averaged wideband loopsensitivity can be obtained from wideband loop sensitivity S_(L)(f).

While several embodiments have been described by way of example, it willbe apparent to those skilled in the art that various modifications maybe configured without departing from the spirit of the presentinvention. Such modifications are all within the scope of the presentinvention, as defined by the appended claims.

NUMERICAL SYSTEM

-   113 acoustic probe-   117A transducer array-   117 acoustic transducer-   200 sine burst generator-   204 reference signal-   208 water bath-   212 acoustic mirror-   214 transmitted acoustic sine burst wave-   218 reflected sine burst wave-   224 echo signal-   400 wideband reference signal of negative-going unipolar pulse-   404 energy spectrum of wideband reference signal of negative-going    unipolar pulse-   500 wideband reference signal of positive-going unipolar pulse-   504 energy spectrum of wideband reference signal of positive-going    unipolar pulse-   600 frequency response of acoustic transducer-   700 wideband reference signal of negative-positive bipolar pulse-   704 energy spectrum of wideband reference signal of    negative-positive bipolar pulse-   800 wideband reference signal of positive-negative bipolar pulse-   804 energy spectrum of wideband reference signal of    positive-negative bipolar pulse-   900 frequency response of acoustic transducer-   1000 pulse generator-   1004 transmitted wideband acoustic wave-   1008 reflected wideband acoustic wave-   1100 wideband echo signal based on negative-going unipolar pulse-   1200 wideband echo signal based on positive-going unipolar pulse-   1300 wideband echo signal based on negative-positive bipolar pulse-   1400 wideband echo signal based on positive-negative bipolar pulse-   1700 system-   1701 pulse generator-   1702 signal processing unit-   1704 transducer selector-   1706 control unit-   1707 firmware-   1708 program memory-   1709 storage-   1730 output devices

NOTATION Reference Signal

-   (V_(ppr)) peak-to-peak voltage of reference signal-   (E_(r)) energy of reference signal; E_(r)= 1/50∫V_(r)(t)²dt=    1/50∫|{circumflex over (V)}_(r)(f)|²df-   (BW_(r)) bandwidth of reference signal;-   (D_(r)) energy density of reference signal;

$D_{r} = \frac{E_{r}}{{BW}_{r}}$

-   V_(r)(t) wideband reference signal;-   {circumflex over (V)}_(r)(f) Fourier Transform of the wideband    reference signal V_(r)(t);-   1/50|{circumflex over (V)}_(r)(f)|² energy spectrum of wideband    reference signal;

Echo Signal

-   (V_(ppe)) peak-to-peak voltage of echo signal;-   (E_(e)) energy of echo signal; E_(e)= 1/50∫V_(e)(t)²dt=    1/50∫|{circumflex over (V)}_(e)(f)|²df-   (BW_(e)) bandwidth of echo signal;-   (D_(e)) energy density of echo signal;

$D_{e} = \frac{E_{e}}{{BW}_{e}}$

-   V_(e)(t) wideband echo signal;-   {circumflex over (V)}_(e)(f) Fourier Transform of the wideband echo    signal V_(e)(t);-   1/50|{circumflex over (V)}_(e)(f)|² energy spectrum of wideband echo    signal;

Definition

-   {circumflex over (X)}(f) normalized loop frequency response

${{\hat{X}(f)}\overset{def}{=}\frac{{\hat{V}}_{e}(f)}{{\hat{V}}_{r}(f)}};{{\hat{X}(f)}\overset{def}{=}{{{\hat{V}}_{e}(f)}/{{\hat{V}}_{r}(f)}}};$

-   X(t) normalized loop time response; Inverse Fourier Transform of the    {circumflex over (X)}(f)    -   X(t)        Inverse Fourier Transform of the {circumflex over (X)}(f)-   S_(L)(f) wideband loop sensitivity is defined as an absolute square    of the {circumflex over (X)}(f) in decibel;    -   S_(L)(f)        10 log|{circumflex over (X)}(f)|²-   (S_(LC)) characteristic loop sensitivity

$S_{LC}\overset{def}{=}{10\;{\log\left( \frac{D_{e}}{D_{r}\;} \right)}}$

-   G (t) Inverse Fourier Transform of the √{square root over    ({circumflex over (X)}(f))};    -   G(t)=Inverse Fourier Transform of the √{square root over        ({circumflex over (X)}(f))}    -   self-deconvolution of the X(t); G (t)=Self deconvolution of the        X(t)-   B(t) an optimum drive signal on energy efficiency basis for the    acoustic transducer;    -   B(t)        α*G(t), wherein a coefficient α is determined to multiply the        function G(t).

What is claimed is:
 1. A system for measuring a wideband loopsensitivity for an acoustic transducer among a plurality of acoustictransducers in a wideband acoustic probe, the system comprising: a pulsegenerator; and a control unit electrically coupled to the pulsegenerator, wherein the pulse generator is configured to be selectivelyelectrically coupled to a predetermined load for generating, by thepulse generator, a first pulse to create a wideband signal as areference signal, and the control unit includes a memory storing thereina program or firmware for causing the control unit to obtain a widebandreference signal V_(r)(t) as a reference signal for an acoustictransducer in the wideband acoustic probe, and obtain a function{circumflex over (V)}_(r)(f) that is a Fourier Transform of the widebandreference signal V_(r)(t).
 2. The system as claimed in claim 1, whereinthe first pulse is one of a unipolar pulse and a bipolar pulse.
 3. Thesystem as claimed in claim 2, wherein the unipolar pulse is one of anegative-going pulse and a positive-going pulse.
 4. The system asclaimed in claim 2, wherein the bipolar pulse is a negative-going pulsefirst and a positive-going pulse second.
 5. The system as claimed inclaim 2, wherein the bipolar pulse is a positive-going pulse first and anegative-going pulse second.
 6. The system as claimed in claim 1,wherein the control unit is further configured to store the function{circumflex over (V)}_(r)(f) in the memory.
 7. The system as claimed inclaim 1, wherein the pulse generator is configured to be selectivelyelectrically coupled to the wideband acoustic probe for generating, bythe pulse generator, a second pulse to create a wideband acoustic wavefrom a first acoustic transducer among the plurality of acoustictransducers in the wideband acoustic probe, and the control unit isconfigured to obtain a wideband echo signal V_(e)(t) after the widebandacoustic wave being reflected from an acoustic mirror, and obtain afunction {circumflex over (V)}_(e)(f) that is a Fourier Transform of thewideband echo signal V_(e)(t).
 8. The system as claimed in claim 7,wherein the control unit is configured to define a normalized loopfrequency response {circumflex over (X)}_(f)(f) for the first acoustictransducer as follows:${\hat{X}(f)}\overset{def}{=}{\frac{{\hat{V}}_{e}(f)}{{\hat{V}}_{r}(f)}.}$9. The system as claimed in claim 8, wherein the control unit isconfigured to define a wideband loop sensitivity S_(L)(f) which is afunction of frequency for the first acoustic transducer as follows:S _(L)(f)

10 log|{circumflex over (X)}(f)|².
 10. The system as claimed in claim 9,wherein the control unit further has a storage device, and is configuredto store the wideband loop sensitivity S_(L)(f) in the storage device.11. The system as claimed in claim 10, wherein the control unit isconfigured to output the wideband loop sensitivity S_(L)(f) stored inthe storage device.
 12. The system as claimed in claim 10, wherein thecontrol unit is configured to sequentially or randomly define thewideband loop sensitivity S_(L)(f) for each and all of the plurality ofacoustic transducers in the wideband acoustic probe.
 13. The system asclaimed in claim 12, wherein the control unit is configured to, aftersequentially or randomly obtaining a plurality of wideband loopsensitivity S_(L)(f) corresponding to the plurality of acoustictransducers in the wideband acoustic probe, store the plurality ofwideband loop sensitivity S_(L)(f) in the storage device.
 14. The systemas claimed in claim 13, wherein the control unit is configured to outputat least one of the plurality of wideband loop sensitivity S_(L)(f)stored in the storage device.
 15. The system as claimed in claim 1,further comprising: the wideband acoustic probe.
 16. A method formeasuring a wideband loop sensitivity for an acoustic transducer among aplurality of acoustic transducers in a wideband acoustic probe, themethod using a pulse generator and a control unit electrically coupledto the pulse generator, the control unit including a memory storingtherein a program or firmware, the method comprising: electricallycoupling a predetermined load to the pulse generator; generating, by thepulse generator, a first pulse to create a wideband signal as areference signal; obtaining, by the control unit, a wideband referencesignal V_(r)(t) as a reference signal for an acoustic transducer in thewideband acoustic probe; and obtaining, by the control unit, a function{circumflex over (V)}_(r)(f) that is a Fourier Transform of the widebandreference signal V_(r)(t).
 17. The method as claimed in claim 16,further comprising: removing the predetermined load from the pulsegenerator; electrically coupling the wideband acoustic probe to thepulse generator; generating, by the pulse generator, a second pulse tocreate a wideband acoustic wave from a first acoustic transducer amongthe plurality of acoustic transducers in the wideband acoustic probe;obtaining, by the control unit, a wideband echo signal V_(e)(t) afterthe wideband acoustic wave being reflected from an acoustic mirror; andobtaining, by the control unit, a function {circumflex over (V)}_(e)(f)that is a Fourier Transform of the wideband echo signal V_(e)(t). 18.The method as claimed in claim 17, further comprising: defining, by thecontrol unit, a normalized loop frequency response {circumflex over(X)}(f) for the first acoustic transducer as follows:${\hat{X}(f)}\overset{def}{=}{\frac{{\hat{V}}_{e}(f)}{{\hat{V}}_{r}(f)}.}$